Anonymous claimed a new accomplishment today: its first physical denial-of-service attack.

The Bay Area Rapid Transit District police closed at least four San Francisco subway stations this evening following a short, peaceful protest at the Civic Center stop, forcing hordes of commuters to trudge up and down Market Street in search of an open station or an alternate way home.

Cell service remained accessible this evening. Meanwhile, the U.S. Federal Communications Commission said earlier today that it would review BART's shutting off cell service in its stations last week.

The online activist collective Anonymous called for the demonstration at Civic Center station to protest fatal BART police shootings and the subway operator's cutting off of cell service last Thursday afternoon in an attempt to head off a previous protest.

Protesters are angry about the fatal shooting of 45-year-old Charles Blair Hill on July 3 by BART officers in Civic Center station, and the January 1, 2009, fatal shooting of Oscar Grant by BART officers. His shooting--while he was restrained, unarmed, and on the ground--was captured on video from cell phones and cameras and widely distributed on the Internet.

About a dozen or so visible protesters, some carrying signs and one in a Guy Fawkes mask, showed up shortly after 5 p.m. PT today in the Civic Center station, surrounded by members of the media. "It's like a media circus down here," one bystander remarked, no doubt echoing what must have been going through a few minds at the event.

After protesters chanting "No Justice No Peace, Disband the BART police" tried to hold the doors open to a train, BART police cleared out the station and shut it down around 5:30 p.m.

No arrests were made, said Dan Hartwig, deputy chief of police at BART. "We shut down the station because we didn't want to jeopardize the safety of passengers and BART employees," he told reporters. "The platform was becoming (crowded and) unsafe... I'm not opposed to them expressing their First Amendment Rights."

While the Anonymous group publicized the event (and likely was behind an intrusion into a BART Web site over the weekend), many of the protesters seemed to be unaffiliated with the activists.

"I'm not part of any group," said a college student who wanted to be identified only by last name of "Capurro." "I'm just disgusted by the violence we've seen from the BART police."